GETTING INTO SPACE

The most direct means of overcoming Earth's gravity and putting a payload, or cargo, into space is to launch it on a rocket. The velocity required is about 17,500 miles per hour (28,000 km/h). The rocket's thrust must be greater than its weight, so even a small cargo uses a lot of fuel.

EXPLORE

Seeking and investigating sources of gamma rays, the most energetic form of radiation, was the objective of COS-B, launched in 1975 by the European Space Agency. The mission ran until 1982. In April 1991, the Compton Gamma Ray Observatory set out to explore further, particularly to identify sources of mysterious gamma-ray bursts.

THE BIG PICTURE

One of the most significant observations of the twentieth century was made in the early 1990s by the Cosmic Back-ground Explorer. COBE measured the feeble back-ground glow thought to be remnant radiation from the Big Bang—the explosion that created the universe.